Keeping data safe during transmission and handling is critical. With APIs accounting for 71% of web traffic, following best practices is essential to protect your endpoints.

Use HTTPS/TLS Encryption

HTTPS with TLS encryption is the cornerstone of secure API communication. Yet, only 45% of API developers currently use HTTPS for data transmission - a sharp drop from 74% in 2023. This decline is alarming, especially given that 84% of security professionals reported at least one API security incident in the past year.

To ensure secure communication, require TLS 1.2 or higher and disable outdated protocols. Use strong certificates, such as a 2048-bit RSA key or ECC certificate, issued by a trusted Certificate Authority. Redirect all HTTP traffic to HTTPS to eliminate vulnerabilities.

"Mutual TLS certificates, like Mutual SSL X.509, are the most effective and widely used digital certificates for APIs." - GlobalSign[9]

Enhance security further by enabling HTTP Strict Transport Security (HSTS) and Perfect Forward Secrecy in your cipher suite. HSTS ensures browsers only connect via HTTPS for a specified duration, reducing the risk of man-in-the-middle attacks during initial connections.

Automate certificate renewals and centralize their management through API gateways. These gateways streamline processes by consolidating certificate handling, authentication, and encryption into a single control point.

"You cannot be efficient if [you have] multiple products, multiple technologies, that are actually not connected. [...] You need one solution. Consolidate - and only then [can you] be actually efficient and effective with your cloud security program." - Assaf Rapport, Wiz co-founder and CEO

By implementing these strategies, you establish secure communication channels that reduce the risk of data exposure.

Limit Data Exposure

Excessive data exposure occurs when APIs return more information than necessary, making it one of the top three API security threats according to OWASP. This issue is not just theoretical; breaches like those involving British Airways and HealthEngine highlight the real-world consequences of overexposed data.

To prevent this, it's essential to examine every layer of your API where excessive data exposure can occur. Pay close attention to:

• Error Pages: Ensure they don’t leak stack traces, debug details, or sensitive backend information.

• URL Strings: Avoid embedding sensitive data in URLs, as these can be logged or cached by browsers and intermediaries.

• API Responses: Scrutinize response payloads for unnecessary fields, especially those revealing internal IDs or confidential information.

• Data in Transit: Encrypt data during transmission to prevent interception.

• Data at Rest: Store only what you need, with appropriate encryption and access controls.

• Client-Side Filtering: Never rely on the client to filter out sensitive data—this should always be enforced server-side.

To combat this, avoid leaving sensitive data filtering to the client. Instead, use server-side filtering to tailor API responses based on user roles and permissions. Regularly review use cases to ensure API responses include only the data required for functionality.

Implement data masking techniques to obscure sensitive information in API responses. These methods should be irreversible, repeatable, and consistently applied across all APIs - not just those identified as handling sensitive data. Tools like GraphQL can also help by enabling clients to request only the specific data they need, reducing unnecessary exposure.

"Data minimization is a fundamental principle in data privacy and protection. It's about collecting and holding onto the bare minimum of personal information needed and retaining it for the shortest duration possible." - Gil Dabah, CEO & Co-founder, Piiano

Establish content-based security policies to restrict data types included in API responses. Additionally, implement data retention policies that ensure data is stored only as long as necessary. Regularly analyzing API responses can help identify and remove any unnecessary or sensitive data.

Validate Input and Sanitize Output

Even with secure communication practices in place, robust input validation and output sanitization are essential to prevent vulnerabilities caused by poorly handled user input.

Server-side validation is non-negotiable - never rely on client-side validation for security. Validate data as early as possible, ideally as soon as it is received from external sources. Use both format checks and context verification to ensure data integrity.

Whitelisting, where only pre-approved values are accepted, is far more effective than blacklisting, reducing vulnerabilities by 66%. Additionally, data annotations and custom filters can cut injection attacks by 85%. Use parameterized queries in database interactions to guard against SQL injection attacks, and validate data from third-party APIs before incorporating it into your systems.

Output encoding is equally critical to prevent Cross-Site Scripting (XSS) attacks. Encode user inputs before including them in responses, and implement Content Security Policies (CSPs), which can reduce the success rate of XSS attacks by over 70%. Combining CSPs with proper output encoding creates a strong defense against injection threats.

Stay up-to-date by regularly updating sanitization libraries to incorporate the latest security patches. Enable strict mode in programming languages like PHP, JavaScript, and SQL, and consult resources such as the OWASP Web Testing Guide for comprehensive advice. By combining validation, sanitization, and encoding, you can significantly lower the likelihood of successful exploits.

Guard Against Parameter Tampering

Parameter tampering occurs when attackers manipulate URL parameters, form fields, cookies, or HTTP headers to gain unauthorized access or modify application behavior. A surprisingly simple change—altering a single value in a URL query string, for example—can open the door to sensitive information or restricted actions if proper defenses aren't in place.

Fortunately, several practical steps help close these loopholes before attackers exploit them:

• Rigorous Data Validation: Enforce strict validation rules using regular expressions or format whitelists, ensuring only properly structured values make it into your system. This goes beyond casual checks—every parameter, whether visible or tucked away in hidden form fields, deserves thorough scrutiny.

• Minimize Parameter Exposure: Limit the use of sensitive data in URLs and visible form fields. If a parameter truly doesn't need to traverse the client side, keep it on the server. Remove unnecessary data from query strings wherever possible.

• Secure Cookies and Sessions: Encrypt session cookies and set appropriate flags (such as HttpOnly and Secure) to keep attackers from hijacking authentication tokens via tampered requests.

• Context-Aware Access Controls: Never trust client-supplied parameters to identify users or roles. Always check server-side state and permissions before granting access or processing sensitive actions.

By systematically validating input, reducing client-side exposure, and locking down session integrity, you dramatically reduce the attack surface available for parameter tampering. These proactive controls round out your API security posture and safeguard your systems against one of the most underappreciated vectors in the wild.

Beware of Parameter Tampering

A lesser-known yet impactful security risk: parameter tampering takes place when attackers manipulate request parameters—such as those found in cookies, query strings, form fields, or HTTP headers—to gain unauthorized access or escalate privileges within an API. This technique can compromise even the most well-intentioned systems if left unchecked.

Imagine an attacker tweaking a hidden form field or modifying a URL query string to alter account numbers or escalate user permissions. If your API trusts these parameters without proper validation, you might as well be handing over the keys to your digital front door.

To curb parameter tampering risks, consider these best practices:

• Enforce strict server-side validation: Use regular expressions and context checks to verify incoming data, ruling out malicious alterations before they do harm.

• Whitelist accepted parameter values and formats: Only permit parameters and data types that you expect—no surprises welcome.

• Limit sensitive data in URLs: Avoid sending confidential info through query strings, as these can be easily intercepted or modified.

• Encrypt and secure cookies: Ensure session cookies are both encrypted and set with appropriate flags (e.g., HttpOnly, Secure) to prevent tampering.

• Keep sensitive fields server-side only: Don’t rely on hidden form fields for important data; if you must transmit, always validate on the server.

By implementing these guidelines, you reduce the attack surface and ensure that your API responds only to intended, authenticated requests—keeping would-be tamperers firmly locked out.

Common Targets in Parameter Tampering

When it comes to parameter tampering, attackers often focus on manipulating key components that influence API behavior and access control. The usual suspects include:

• Cookies: These store user session information and authentication tokens. Modifying them may grant unintended privileges or bypass restrictions.

• Form fields: User-supplied form data, whether in login forms or data submissions, can be altered to access or modify forbidden resources.

• URL query strings: Parameters in the URL can be tweaked to reveal hidden data, trigger unauthorized actions, or bypass security checks.

• HTTP headers: Headers like Authorization or custom identifiers are frequently targeted to escalate privileges or impersonate users.

Vigilantly monitoring and validating each of these vectors is crucial. An attacker who slips past weak controls in any of these areas could gain access to sensitive functions or data well outside their intended boundaries.

Enforce Allowed HTTP Methods

Locking down your API's HTTP methods is a key—yet often overlooked—line of defense. Each API endpoint should only accept the HTTP methods strictly necessary for its function. For example, an endpoint designed to retrieve information (like a user's account balance) should only permit safe, read-only methods such as GET.

Why does this matter? If non-essential methods like POST, PUT, or DELETE aren't properly restricted, attackers could exploit these to submit unauthorized changes, tamper with data, or even delete resources outright. It's the digital equivalent of letting anyone with a key not only enter a building to check the mail, but also rearrange the furniture—or worse, set fire to it.

To reduce risk, configure your API to reject requests using disallowed methods by automatically responding with a 405 Method Not Allowed status. This keeps business logic predictable and prevents accidental or malicious misuse. Frameworks like Express.js, Django REST Framework, and ASP.NET Core make enforcing HTTP methods straightforward—don’t leave the door open wider than it needs to be.

Pair this approach with clear API documentation and regular testing to confirm only permitted operations are accessible. This small yet essential step sharply narrows the attack surface and helps ensure your APIs behave as intended.

Test for SQL Injection Vulnerabilities

SQL injection attacks remain a classic — and very effective — tactic used by attackers to infiltrate APIs by manipulating backend database queries. If an API endpoint fails to properly validate and handle user-supplied input, an attacker can craft specially formed payloads that trick the database into running rogue commands. The consequences? Data theft, unauthorized data modification, and sometimes even complete compromise of the backend environment.

To proactively guard against these threats, it's crucial to rigorously test your API endpoints for SQL injection flaws. This process simulates typical attack patterns to ensure dangerous queries cannot slip through. Here’s how you can approach SQL injection testing:

• Leverage open source tools:
  A variety of tools cater specifically to testing SQL injection vulnerabilities in APIs, each bringing a slightly different angle to the table:

  • SQLmap: This open-source tool automates the detection and exploitation of SQL injection vulnerabilities, streamlining the process for penetration testers of all levels.

  • SQLninja: Best suited for targeted testing against Microsoft SQL Server, SQLninja helps simulate sophisticated attacks that could give an intruder database control.

  • SQLSus: Lightweight yet powerful, SQLSus offers a flexible approach for security professionals looking to identify and exploit SQL injection points, especially in MySQL environments.
    
    

• Automated and manual checks: Combine automated scanning with manual testing, especially on high-value endpoints and those handling user credentials or financial operations.

• Review API error messages: Excessive or verbose database errors can provide clues to an attacker. Ensure APIs leak minimal information on failures.

Perform SQL injection testing as a regular part of your security assessments, especially after releases or updates affecting input handling. By staying vigilant and using established tools, you can keep your APIs defended against one of the most persistent—and costly—attack vectors. Integrating these tools into your automated or manual testing workflows ensures that potentially costly flaws are found and resolved swiftly. By combining multiple solutions, you can achieve broader coverage and a more robust assessment of your API’s resilience to SQL injection attacks.